This invention relates to a method of laminating three or more thermoplastic resin sheets by utilizing sonic bonding.
Recently, in clinical assay field, the advantages of the dry analysis using chemical analytical slide have been appreciated in simplicity and rapidity, and this method has widely been utilized.
In general, the chemical analytical slide is, as shown in FIG. 11, composed of upper frame sheet 1 and lower frame sheet 2 locating on the upside and the underside respectively, and middle frame sheet 3 and chemical analytical film 4 disposed therebetween. Upper frame sheet 1 is provided with a spotting aperture 5 for spotting sample liquid in the center, and lower frame sheet 2 is provided with a measuring aperture 6 for measuring the color produced in chemical analytical film 4 in the center. While, middle frame sheet 3 is provided with a film aperture 7 shaped to receive chemical analytical film 4. These three frame sheets are bonded to each other to form an integral element.
Upper frame sheet 1, middle frame sheet 3 and lower frame sheet 2 are, in general, made of plastic resin. Though these frame sheets may be produced by injection molding, the sheet web called "hoop material" is preferable in view of production efficiency. The state of manufacturing chemical analytical slides using plastic hoop materials is illustrated in FIG. 10. In the drawing, lower frame hoop material 9 is punched by a punching apparatus (not illustrated) to form measuring aperture 6, and while, middle frame hoop material 10 is also punched by a punching apparatus (not illustrated) to form film aperture 7. Then, middle frame hoop material 10 is thermally bonded to upper frame hoop material 9 at the first ultrasonic horn 12. Subsequently, chemical analytical film 4 is fitted in film aperture 7, and upper frame hoop material 11 provided with spotting aperture 5 by a punching apparatus (not illustrated) is thermally bonded to middle hoop material 10 at the second ultrasonic horn 13. The laminate of the hoop materials thus prepared is punched so that the chemical analytical slides are formed separately.
In this process, both of middle frame sheet web 10 and upper frame sheet web 11 have to be provided with projections on one surface respectively formed previously, for example, by embossing (as described in U.S. Pat. No. 4,230,757). As shown in FIG. 9, middle frame sheet web 10 was superposed on lower frame sheet web 9 having flat surfaces on both sides so as to face the embossed surface 14 of middle frame sheet web 10 to lower frame sheet web 9. Then, both web sheets were pressed to bond each other at the first ultrasonic horn 12. Upper frame sheet web 11 was then superposed on middle frame web sheet 10 to face the embossed surface 14 of upper frame web sheet 11 to middle frame web sheet 10, and they were bonded by the second ultrasonic horn 13 under pressure.
Since such a conventional method requires two sheet webs embossed previously and the equipment for embossing sheet webs in big, necessity of embossing process causes high cost of the method.